Communication systems provide services to a plurality of terminals to enable the terminals to communicate with each other. Especially, a communication link can be established between different terminals in order to exchange information in form of audio signals, text messages, images, videos, data or a mixture thereof. One example of the communication link is a call session. When a call session is established between terminals, users associated with these terminals can e.g. talk to each other or exchange information in other ways.
A special form of call session is an emergency session. Emergency sessions are special call sessions that are established between an emergency center and a terminal whose user requests emergency service. The emergency center is for example located at the local police station or the local fire department. The requested emergency service may comprise medical assistance in form of an ambulance or assistance with fire/accident by firefighters. An example of an emergency center is a so-called Public Safety Answering Point (PSAP) as known from 3GPP.
Emergency sessions have special properties compared to normal call sessions between terminals. The main reason behind this is that emergency sessions are handled in a special way and processed only by the visited network in which a terminal is active (and not by the home network associated with the user of the terminal as this is the case for normal call sessions). In many communication systems, emergency sessions are prioritized over other services and have a special emergency registration. Furthermore, emergency sessions are established using a simplified procedure e.g. by refraining from authenticating the calling terminal. Thereby, terminals can establish an emergency session even without a subscription. An example of emergency sessions in a prior art mobile communication system is described in the technical specification 3GPP TS 23.167.